The present invention is directed to a grab bucket of the type which is suspended from a cable so that it may be lowered to a pile of material such as sand or gravel to grab and lift an amount of such material. The bucket is designed to open and close whereby the bucket, in the open position, is lowered into the pile, closed to capture a portion of the material, and then lifted by the cable to remove the captured material to another location.
Pursuant to one prior art proposal disclosed in the F.R. Germany Publication DE-AS No. 22 00 799, an electrical switching unit is provided to control the operation of a grab bucket. The switching unit automatically and temporarily energizes the lifting motor to facilitate a quick closing of the bucket. However, the "grabbing" quality of the buckets generally used in apparatuses of this type is so effective that such buckets tend to dig themselves into the pile of material as they close so that the bucket becomes overfilled with material. Typically, the excess material spills over the open top of the bucket. Moreover, the burrowing effect of the bucket closing motion impedes a fast and full closing of the bucket since the amount of material within and surrounding the bucket offers considerable resistance to the closing motion. Consequently, a considerable amount of energy is required to effect a full closing and despite a high energy input, the bucket may still emerge from the pile not fully closed.
It is a primary objective of the present invention to provide a grab bucket apparatus of the above-described type including new and improved electrical control means to overcome the problems of the prior art while providing a fast and efficient bucket operation with decreased energy consumption. Pursuant to the invention, a slackline limit switch detects a slacking condition in the bucket-lifting cable, as when the open bucket has engaged the top of the pile. The limit switch thereupon automatically de-energized the lowering motion for the cable and energizes the means for closing the bucket.
Pursuant to an important feature of the invention, the slackline limit switch also energizes several timer relay means set to time out at various times to initiate a predetermined sequence of bucket operations. More specifically, the timer relay means are electrically associated with one another and other electrical control devices to automatically control and co-ordinate the closing and lifting of the grab bucket. When the closing of the bucket commences, several timer relays are activated to commence timing. Before full closure of the bucket, one of the timers times out thereby energizing the hoisting motor to commence the lifting of the bucket from the pile. A second timer relay times out after the bucket has been hoisted above the pile to stop the lifting motion so that the bucket is positioned slightly above the pile just before it is fully closed. In this manner, there will be no resistance from the pile to the closing bucket motion so that the bucket may be fully closed with minimal energy consumption. Another timer then times out to re-energize the hoisting mechanism so that the bucket may be raised to its destination.
It has been found that a grab bucket of the type utilized in the system of the present invention is completely filled with the material grabbed during the first quarter of the closing process. Accordingly, by lifting the bucket from the pile before a full closure of the bucket, pursuant to the teaching of the invention, there is no loss in the amount of material grabbed while there is considerable savings in the amount of energy needed to fully close the bucket. Thus, the present invention teaches a means for utilizing a grab bucket to its fullest potential while providing a highly energy-efficient operation.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment of the invention together with the accompanying drawings.